1. Field of the Invention
The present invention relates to a keypad used in a portable terminal, and more particularly to a keypad and a keypad assembly having a light guide panel.
2. Description of the Related Art
A keypad used in a portable terminal typically includes an elastic pad plate, a plurality of key buttons formed on the upper surface of the elastic pad with characters printed on the upper surface thereof, respectively, and a plurality of protrusions (or actuators) formed on the lower surface of the elastic pad. This type of portable terminal normally has about 15–20 light emitting devices serving as a back light of the keypad.
FIG. 1 is a sectional view showing a keypad assembly according to the prior art. As shown, the keypad assembly 100 includes a keypad 110, a switch board 150, and a plurality of light emitting diodes(LEDs) 170.
The keypad 110 includes an elastic pad 120 having the shape of a plate, a plurality of key buttons 140 formed on the upper surface 122 of the elastic pad 120 with characters, numbers, etc., printed on the upper surface thereof, respectively, and a plurality of protrusions 130 formed on the lower surface 124 of the elastic pad 120, which is opposite to the upper surface 122 of the elastic pad 120. Each of the protrusions 130 is aligned with the center portion of the corresponding key button 140. The elastic pad 120 has a plurality of grooves 126 formed on the lower surface 124 thereof. The grooves 126 are positioned around the respective protrusions 130 to prevent the LEDs 170 from interfering with the protrusions 130.
The switch board 150 has a plate-shaped PCB (Printed Circuit Board) 155 and a plurality of switches 160 formed on the upper surface of the PCB 155 facing the keypad 110. Each switch 160 is comprised of a conductive contact member 162 and a conductive dome 164 covering the contact member 162 completely.
The plurality of LEDs 170 are mounted on the upper surface of the PCB 155, and each LED 170 is positioned to be covered by the corresponding groove 126 of the elastic pad 120.
When the user presses one of the key buttons 140, the portion of the keypad 110 positioned beneath the pressed key button 140 deforms towards the switch board 150. As a result, one of the protrusions 130 corresponding to the deformed portion presses the corresponding dome 164, thus providing an electrical contact with the corresponding contact member 162.
Due to the operation of the switches 160 in the vicinity, the LEDs 170 must not be positioned beneath the corresponding key buttons 140. Light outputted from the respective LEDs 170 passes through the elastic pad 120 and illuminates the respective key buttons 140 at an oblique angle. As a result, the key buttons 140 are dimly illuminated in a non-uniformly fashion. In particular, the center of each key button 140 looks darker, and the periphery thereof looks brighter. If more LEDs are installed to enhance an uniform illumination of the key buttons 140, power consumption and manufacturing cost increase.